Steerable catheter with shaft load distributions

ABSTRACT

A steerable catheter system may include a flexible elongate catheter body, a drive mechanism at the proximal end of the catheter body, and at least one group of pullwires extending along a length of the catheter body. The catheter body may include a distal articulating section and a proximal non-articulating section. Each group of pullwires includes at least two pullwires, and each of the pullwires is anchored at a first end to the distal end of the catheter body and at a second end to the drive mechanism. The pullwires of each group are positioned close to one another in the catheter wall to concentrate the forces and cause deflection along the articulating section of the catheter body and diverge away from one another to reach a more separated distribution around a circumference of the catheter body to distribute the forces and prevent deflection along the non-articulating section.

FIELD

The invention relates generally to minimally-invasive instruments andsystems, such as manually or robotically steerable catheter systems.More specifically, the invention relates to steerable catheter systemsfor performing minimally invasive diagnostic and therapeutic procedures.

BACKGROUND

Robotic steerable catheter systems typically include a flexible cathetershaft having an articulation section at a distal tip. These systems aredesigned to facilitate access to distal target sites in the humananatomy and require simultaneous articulation of the distal tip withcontinued insertion or retraction of the catheter. Pullwire basedarticulating catheters typically have pullwires passing through theshaft, and each pullwire is anchored to a fixed location around thedistal tip. Each pullwire is then selectively tensioned to articulatethe tip in various directions. As such, the catheter shaft should belaterally flexible to follow the curvature in the anatomy, but axiallyrigid to resist the high axial loads being applied to articulate thecatheter tip.

Increasing the lateral flexibility of the catheter, however, introducescatheter navigation problems that may not otherwise occur when thecatheter is laterally stiff. For example, many steerable catheters havea multitude of free floating pullwires (e.g., four pullwires),circumferentially spaced in the wall of the catheter and attached to acontrol ring embedded in the distal end of the catheter. If fourpullwires are provided, the pullwires may be orthogonally spaced fromeach other. Each of these pullwires is offset from the center axis ofthe catheter, so that when a wire is tensioned to steer the catheter'sdistal tip under ideal conditions, the resulting bending moment causesthe distal tip to articulate in the direction of the pullwire that istensioned. However, the compressive forces from the tensioned pullwireon the relatively flexible catheter shaft also cause the shaft tocompress and/or to experience other undesired effects.

For example, flexible shafts adapt to the shape of the anatomy as theytrack through it. This results in a curved shaft. The curvature of thecatheter shaft may make the articulation performance of the catheterunrepeatable and inconsistent. In particular, because the pullwires areoffset from the neutral axis of the catheter shaft, bending the cathetershaft causes the pullwires on the outside of the curve to tighten whilethe pullwires on the inside of the curve slacken. As a result, theamount of tension that should be applied to the pullwires in order toeffect the desired articulation of the distal tip varies in accordancewith the amount of curvature applied to the catheter shaft.

Referring to FIGS. 1A and 1B, a prior art catheter 10 with anarticulating distal portion 11 (or “distal tip”) is shown, to illustrateanother example of the challenges faced when articulating a catheter ina body. As illustrated, one challenge is that the articulated distal tip11, when bent, tends to align its curvature with the curvature of theshaft of the catheter 10. In particular, as shown in FIG. 1B, operatingor tensioning a pullwire 14 on the outside edge of a bend may cause thecatheter 10 to rotate or twist. This rotation or twist phenomenon isknown as “curve alignment,” because the distal tip 11 and shaft of thecatheter 10 tend to rotate until the tensioned pullwire 14 is on theinside of the bend, and the curve in the distal tip 11 is aligned withthe curvature in the shaft. That is, when the proximal shaft section ofthe catheter 10 is curved (as it tracks through curved anatomy), and thedistal tip 11 is commanded to articulate, the curvature in the shaft canimpact the articulation performance of the distal tip 11.

In FIG. 1A, the pullwire 12 that is pulled happens to be on the insideof the bend of the catheter shaft 10, and the distal tip 11 articulatesto the left as intended. However, if it is desired to bend the distaltip 11 in a direction that is not aligned with the curvature of theproximal portion of the catheter 10, (e.g., if it is desired to bend thedistal tip 11 to the right, as shown by the dotted distal tip outline inFIG. 1B), the pullwire 14 on the outside of the bend is pulled. Atorsional load (T) is applied to the shaft as tension increases on thepullwire 14 on the outside of the bend. This torsional load rotates theshaft until the pulled pullwire 14 is on the inside of the bend. Asshown in FIG. 1B, the initial position of the outer pullwire 14 isdepicted by a dashed line, and the rotated position followingapplication of the torsional load is depicted by the solid line. Ineffect, the tensioned pullwire 14 on the outside of the bend takes thepath of least resistance, which may often rotate the shaft to the insideof the bend (as shown by the thick, solid-tipped arrows in FIG. 1B),rather than articulating the distal tip 11 as the user intends. Thisresults in the distal tip 11 pointing to the left, as shown in thesolid-line version of the distal tip 11, even though the user wanted tobend the distal tip 11 to the right, as shown in the dotted-lineversion. This unintentional rotation of the shaft causes instability ofthe catheter distal tip 11 and prevents the physician from being able toarticulate the distal tip 11 to the right. In other words, no matterwhich direction the catheter distal tip 11 is intended to be bent, itmay ultimately bend in the direction of the proximal curve. Thisphenomenon is known as curve alignment, because the pullwire 14 that isunder tension puts a compressive force on both the proximal and distalsections of the catheter 10 causing both the proximal and distalcurvatures to align in the same direction in order to achieve the lowestenergy state.

The operator may attempt to roll the entire catheter 10 from theproximal end in order to place the articulated distal tip in the desireddirection. However, this moves the tensioned inside pullwire 14 to theoutside of the proximal bend, causing further tensioning of the pullwire14. This increased tension on the pullwire 14 on the outside of the bendcan cause an unstable position. The catheter shaft 10 wants to return toa lower energy state and may do so by quickly whipping around to get thetensioned pullwire 14 back to the inside of the bend. In amulti-direction catheter, the operator may attempt to pull a differentpullwire to try to bend the distal tip to the right, but as soon as thetension is built up on that wire, it also wants to spin the distal tiparound and return to the inside of the bend. Continued attempts to tryto find a pullwire to articulate the distal tip against the direction ofcurvature of the catheter shaft may lead to rotation or windup of thecatheter shaft. This stored energy in the shaft can lead to whipping ofthe catheter shaft to return to a lower energy state and may injure thepatient.

FIGS. 2A and 2B illustrate another example of the challenges faced whenarticulating a flexible catheter 10. When performing a steering maneuverwith a flexible catheter 10, the tension on the pullwire(s) causes axialcompression on the catheter shaft, which bends the distal tip 11 of thecatheter 10. This axial compression may cause undesired lateraldeflection in flexible catheter shafts, thereby rendering the cathetermechanically unstable. FIGS. 2A and 2B illustrate how prior art flexibleinstruments exhibit unwanted lateral shaft deflection when one or morepullwires are pulled. In these figures, the pullwires run through thewall of the catheter shaft. An example of ideal articulation performanceis shown in FIG. 2B. If the shaft is made of stiff materials, then thecatheter distal tip 11 is more likely to exhibit ideal articulationperformance. If the catheter shaft is made of more flexible, trackablematerials, then the catheter 10 is more likely to bend as shown in FIG.2A, with bending occurring not only in the distal tip 11, but also alonga length of the catheter shaft. The shaft of the catheter is beingmuscled by the pullwires and experiencing unwanted lateral deflection.

The additional lateral deflection of the shaft of the catheter 10 may beundesirable, because it may unintentionally force the catheter againstthe anatomy. This has the potential for injury and distracts theoperator, because he or she must constantly monitor what the shaft isdoing. If the shaft is in a constrained position within the arteries,such as passing over the iliac bifurcation, the arterial rigidity maystop the shaft from being muscled by the pullwires. But alternatively,the catheter shaft may be in a more flexible artery, such as the splenicartery, where the catheter may damage or distort the shape of theartery.

Referring to FIGS. 3A-3C, if a catheter 10 is in a large artery or openchamber, such as the aorta or heart, the catheter 10 may have space todeflect. This creates an additional problem, because the more space thecatheter shaft has to deflect, the greater the impact on the amount ofcatheter tip articulation. For example, FIGS. 3A-3C show the catheter 10in three different configurations. In FIG. 3A, both the proximal shaftand the distal articulation tip 11 are straight. In FIG. 3B, a pullwirehas been pulled a distance x, and the articulation tip 11 has bent 90degrees. The proximal shaft has not bent. This may occur, for example,when the shaft is constrained by the anatomy. In FIG. 3C, the pullwirehas been tensioned an equal amount as in FIG. 3B, but the shaft has alsocompressed. Therefore, in FIG. 3C, some of the pullwire displacement hasbeen “used up” to compress the shaft, and hence there is lesscompression of the articulation tip 11. As a result, the articulationtip 11 only bends approximately 80 degrees in FIG. 3C. It would bedesirable to isolate bending to the distal articulation tip 11, to aidin predictability and controllability. In other words, an ideal catheterinstrument would have a distal articulation tip 11 that bends ascommanded and is not dependent on the anatomical path or the stiffnessof the vasculature.

Undesirable lateral motion related to muscling and undesirablerotational motion related to curve alignment both result from the sameforces associated with pullwire tensioning. Each of these mechanicalchallenges contributes to the instability and poor control of thecatheter tip, as well as decreased catheter tracking performance. Somesteerable catheters overcome these problems and resist compressive andtorsional forces by increasing the axial stiffness of the entirecatheter shaft (e.g., by varying wall thickness, material durometer,and/or braid configuration), or alternatively by incorporating axiallystiff members within the catheter shaft to take the axial load. Butthese changes also laterally stiffen the catheter shaft, making it lessmaneuverable, and thereby causing new difficulties in tracking thecatheter through the vasculature of the patient. Therefore, the catheterdesigner is forced to compromise between articulation performance andshaft tracking performance.

Another design intended to overcome the problems of muscling and curvealignment involves locating all the pullwires in the shaft close to theneutral axis, as described in U.S. Pat. No. 8,894,610. This is known asthe “unirail design” for a catheter. While the unirail design locatesall pullwires in one location, it is impossible to locate all pullwiresexactly on the neutral axis, so the catheter continues to experiencesome slight unwanted shaft curvature. Catheter designers typically needto design some lateral stiffness into the catheter shaft, to try tominimize this unwanted curvature. Therefore, the shaft of the unirailcatheter cannot be designed with very low lateral stiffness.

Another strategy is to spiral the pullwires around the circumference ofthe catheter shaft, as described in U.S. patent application Ser. No.14/542,373 (U.S. Patent App. Pub. No. 2015/0164594). This is known asthe helical design and can be used to balance loads in the cathetershaft. However, continuously spiraling the pullwires leads to increasedfriction in the catheter system, and so there is still a tradeoffbetween shaft flexibility and articulation performance.

Other steerable catheters overcome this problem by using free floatingcoil pipes in the wall of the catheter to respectively house thepullwires, thereby isolating the articulation loads from the cathetershaft. (Embodiments and details are described in U.S. patent applicationSer. No. 13/173,994, entitled “Steerable Catheter,” (U.S. Patent App.Pub. No. 2012/0071822), which is expressly incorporated herein byreference in its entirety.) However, the use of coil pipes adds to thecost of the catheter and takes up more space in the shaft, resulting ina thicker catheter wall. Such a design is not appropriate for catheterswith small outer diameters intended for use in narrow vasculature.

Pullwire-based steerable catheters typically incorporate the steeringpullwires into the walls of the catheters, and the catheters must bedesigned to accommodate the thickness and arrangement of the pullwires.Referring to FIGS. 4A-4C, various examples of pullwire-based steerablecatheters 10A-10C are provided, each including steering pullwires12A-12C in the wall of the respective catheter. The diameter of thesteering pullwires 12A-12C usually determines the wall thickness thatcan be achieved. For example, in the embodiment illustrated in FIG. 4A,there are four small pullwires 12A evenly spaced around thecircumference of the catheter 10A, whereas in FIG. 4C, there are threelarger diameter pullwires 12C equally spaced around the circumference ofthe catheter 10C. The embodiment in FIG. 4A has a thinner wall, due tothe smaller diameter of the pullwires 12A. Thinner walls are preferable,because, as shown, they allow for a larger inner diameter (ID) for agiven outer diameter (OD), or a smaller OD for a given ID. In otherwords, thin walls allow for the smallest OD:ID ratio. Advantageously,larger inner diameters allow for delivery of a broader range of tools.Smaller outer diameters allow for access to narrower blood vessels,thereby increasing the number of procedures that can be performed withsteerable catheters. Smaller ODs also allow for smaller incisions inpatients and hence, faster recovery times.

One barrier to achieving a small OD:ID ratio is the diameter of thepullwires. For example, the relatively small pullwires 12A in FIG. 4Ahave less tensile strength than the pullwires of FIGS. 4B and 4C, andthis can limit the articulation force that can be applied to bend thedistal articulation tip. The embodiment in FIG. 4B is an alternativeoption, which uses larger pullwires 12B while maintaining a larger ID.Here, the OD and ID of the catheter 10B are not concentric. There isonly one pullwire 12B, so the wall thickness is thinner in the areaopposite the pullwire 12B to maximize the inner lumen. This catheterembodiment 10B, however, has a reduced degree of freedom (i.e., lessmaneuverability) at the distal tip. Accordingly, each design hassignificant tradeoffs.

Thus, although a number of innovations have been made, major unresolvedchallenges remain when using pullwires to articulate the distal tip of aflexible catheter. It would, therefore, be desirable to have improvedsteerable catheters, designed to particularly address at least some ofthe challenges described above. Ideally, such improved catheters wouldhave a desired combination of stiffness, flexibility, and ease ofarticulation. Also ideally, the catheters would have a desirable innerdiameter and outer diameter to make them suitable for passinginstruments and for advancing through small incisions and vasculature.At least some of these objectives will be addressed by the embodimentsdescribed herein.

BRIEF SUMMARY

Advantageously, various steerable catheter embodiments provided hereinuse multiple pullwires to steer the distal tip (or “articulatingsection”) in a single articulation direction. Those pullwires thendiverge into a more spaced distribution of pullwires in the proximalshaft section (or “non-articulating section”). This results in a bendingmoment in the distal articulating section and no bending moment in theshaft of the catheter. This design can be repeated, so that three ormore sets of pullwires may be used to create an omnidirectionalarticulating section. With this design, the articulating section can beindependently controlled by pullwires, while the catheter experiences noshaft bending or unintended rotation. In other words, this configurationof pullwires allows a catheter shaft to have minimal lateral stiffness,and yet be able to withstand pullwire forces without experiencingunintended bending or rotation. This configuration also allows for themanufacture of thinner walled catheters, because smaller-diameterpullwires may be used in this design, compared to traditional pullwiresystems, resulting in an overall reduction in outer diameter (OD) and/orincrease in inner diameter (ID).

In one aspect of the present disclosure, a steerable catheter system mayinclude a flexible elongate catheter body, a drive mechanism at theproximal end of the catheter body, and at least one group of pullwireswithin a catheter wall of the catheter body, extending along a length ofthe catheter body. The catheter body may include a catheter wall forminga central lumen, a proximal end, a distal end, a distal articulatingsection, and a proximal non-articulating section. Each group ofpullwires includes at least two pullwires, and each of the pullwires isanchored at a first end to the catheter body and at a second end to thedrive mechanism. The pullwires of each group are positioned close to oneanother along the articulating section of the catheter body and divergeaway from one another to reach a more separated distribution along thenon-articulating section.

In some embodiments, the two pullwires in each group are distributeduniformly around the circumference in the non-articulating section. Insome embodiments, each group of pullwires includes three or morepullwires, and the more separated distribution of the three or morepullwires in the non-articulating section means that each pullwire in agiven group is positioned less than 180 degrees away from eachimmediately adjacent pullwire in the given group.

Various alternative embodiments may include any suitable number ofgroups of pullwires and any suitable number of pullwires per group. Forexample, some embodiments may include three groups of pullwires with atleast two pullwires per group, other embodiments may include threegroups of pullwires with at least three pullwires per group, etc.

In some embodiments, the system may also include a robotic instrumentdriver, which includes a splayer comprising multiple pulleys. Each ofthe pulleys is attached to one of the pullwires, and each of the pulleysis configured to be rotated by a motor in the robotic instrument driver.In some of these embodiments, each of the pulleys may be configured tobe rotated to generate tension in the two pullwires, where an increasein tension on all of the at least two pullwires contributes todeflection of the articulating section of the catheter body. Also insome embodiments, the tension on the two pullwires contributes to abending moment in the articulating section of the catheter body whilecancelling the bending moment in the non-articulating section.

In other embodiments, the system may also include a robotic instrumentdriver, where the drive mechanism includes a splayer having multiplepulleys, and where each of the pulleys is attached to one group ofpullwires. Each of the multiple pulleys interfaces with a motor in theinstrument driver to increase tension in the one group of pullwires toarticulate the catheter body. Such embodiments may also include a loadbalancing actuation mechanism for facilitating proportional tensioningof each pullwire within at least one group of pullwires. Examples ofload balancing actuation mechanisms include a two-way whiffletree, athree-way whiffletree, an elastic pullwire, a two-way differential, anda three-way differential.

In some embodiments, the catheter body has a cylindrical shape. In someembodiments, the at least two pullwires of the group of pullwires spiralaround the catheter body along a divergence section, disposed betweenthe articulating section and the non-articulating section, to transitionfrom their positions in the articulating section to their positions inthe non-articulating section.

In another aspect of the present disclosure, a multiple-bend steerablecatheter may include a flexible elongate catheter body and multiplepullwires within a catheter wall of the catheter body, fixed to thedistal end of the catheter body and extending along the catheter body tothe proximal end. The catheter body may include a catheter wall forminga central lumen, a proximal end, a distal end, a distal articulatingsection at the distal end of the catheter body, a proximalnon-articulating section at the proximal end of the catheter body, and aproximal articulating section located between the distal articulatingsection and the proximal non-articulating section. The pullwires areconfigured in groups of at least two pullwires each, and the at leasttwo pullwires of each group are positioned closer to one another in thedistal articulation section than in the proximal articulation section.

Some embodiments include three groups of two pullwires each, where thepullwires in each group are located close to one another in the distalarticulating section and are located directly across from one another inthe proximal articulating section. In alternative embodiments, all ofthe pullwires are located along one side of the catheter body in theproximal non-articulating section. In some embodiments, the pullwires ineach group are located directly across from one another in the proximalnon-articulating section, and the proximal non-articulating section ofthe catheter body is stiffer than the distal articulating section andthe proximal articulating section.

In some embodiments, the at least two pullwires in each group ofpullwires are located in first circumferential positions along thedistal articulating section, second circumferential positions along theproximal articulating section, and third circumferential positions alongthe proximal non-articulating section, where the second circumferentialpositions are farther apart from one another than the firstcircumferential positions. In one such embodiment, the thirdcircumferential positions are the same as the second circumferentialpositions, and the proximal non-articulating section of the catheterbody is stiffer than the distal articulating section and the proximalarticulating section.

Some embodiments of the catheter may include twelve pullwires, which mayinclude a first collection of nine pullwires grouped together in thesecond circumferential position on one side of the catheter body in theproximal articulating section, where the nine pullwires are separatedinto three groups of three pullwires in the first circumferentialposition, with each of the three groups separated from the other twogroups by 120 degrees in the distal articulating section, and where onepullwire from each of the three groups of pullwires is positioned 120degrees from the other two pullwires from each of the three groups inthe third circumferential position in the proximal non-articulatingsection. The twelve pullwires may also include second collection ofthree pullwires uniformly positioned around the catheter body in thefirst circumferential position in the distal articulating section and inthe second circumferential position in the proximal non-articulatingsection, wherein the three pullwires are distributed to an opposite sideof the catheter body from the nine wires in the second circumferentialposition in the proximal articulating section. In these embodiments, thedistal articulating section is configured to articulate when one or twoof the three groups of the first collection of nine pullwires aretensioned with an amount of force equal to an amount of force applied tothe second collection of three pullwires. Also in these embodiments, theproximal articulating section is configured to articulate when thesecond collection of three pullwires is pulled in a first directionuniformly or when the first collection of nine pullwires is pulled in asecond, opposite direction uniformly.

Other embodiments of the catheter may include six pullwires, including afirst collection of three pullwires positioned to articulate the distalarticulating section, such that they are uniformly positioned around thecatheter body in the distal articulating section and positioned to oneside of the catheter body in the proximal articulating section. The sixpullwires may also include a second collection of three pullwirespositioned to articulate the proximal articulating section, such thatthey are uniformly positioned around the catheter body in the distalarticulating section and distributed to one side of the catheter body inthe proximal articulating section at 180 degrees opposite the firstcollection of three pullwires. In some of these embodiments, the distalarticulating section is configured to articulate when one or two of thefirst collection of pullwires are tensioned with an amount of forceequal to an amount of force applied to the second collection of threepullwires. Additionally, the proximal articulating section is configuredto articulate when the second collection of three pullwires is pulled ina first direction uniformly or when the first collection of threepullwires is pulled in a second, opposite direction uniformly.

In yet another embodiment, the catheter may include six pullwires,including three pairs of two pullwires each. Each of the three pairs ofpullwires may be spaced 120 degrees apart from the other two pairs ofpullwires around the catheter body in the first circumferential positionin the distal articulating section, and the two pullwires of each of thethree pairs separate from one another and are positioned 180 degreesopposite each other around the catheter body in the secondcircumferential position in the proximal articulating section. In someembodiments, all six pullwires may be positioned on one side of thecatheter body in the third circumferential position in thenon-articulating proximal section.

In another aspect of the present disclosure, a steerable roboticcatheter system may include an instrument driver, including at least onerotary output shaft, a flexible elongate catheter, including at leastone group of three pullwires attached to and extending along a wall ofthe catheter body, and a drive interface connecting the catheter to theinstrument driver. The drive interface includes a load balancingmechanism configured such that when the at least one rotary output shaftof the instrument driver is rotated, equal tension is applied to thethree pullwires. In some embodiments, the load balancing mechanism mayinclude a three-way differential. The three-way differential may includea sun gear, a ring gear, multiple planetary gears, a first stage fixedto a first of the three pullwires and driven by the sun gear, and atwo-way differential driven by the ring gear. The two-way differentialmay include second and third stages fixed to second and third pullwiresof the three pullwires, respectively. The sun gear may have a diameterthat is half as large as a diameter of the ring gear, such that when theoutput shaft of the instrument driver is rotated, equal tension isapplied to all of the three pullwires.

In yet another aspect of the present disclosure, a steerable roboticcatheter system may include: instrument driver, including at least onerotary output shaft; a flexible elongate catheter, including a catheterbody and at least one group of three pullwires attached to and extendingalong a wall of the catheter body; and a drive interface connecting thecatheter to the instrument driver. The drive interface may include aplanetary gear system, which in turn may include a sun gear, a ringgear, multiple planetary gears, and a two-way differential with a firststage and a second stage. The two way differential is driven by the ringgear, a first pullwire of the three pullwires is attached to the firststage, and a second pullwire of the three pullwires is attached to thesecond stage, and the sun gear has a diameter that is half a diameter ofthe ring gear. A third pullwire of the three pullwires is attached tothe sun gear, such that when the rotary output shaft of the instrumentdriver is rotated, equal tension is applied to all of the threepullwires. Some embodiments may include four rotary output shafts andfour groups of three pullwires each.

In another aspect of the present disclosure, a steerable roboticcatheter system may include: an instrument driver, including at leastone rotary output shaft; a flexible elongate catheter, including acatheter body and at least one group of two pullwires attached to andextending along a wall of the catheter body; and a drive interfaceconnecting the catheter to the instrument driver. The drive interfaceincludes a load balancing mechanism configured such that when the atleast one rotary output shaft of the instrument driver is rotated, equaltension is applied to the two pullwires of the at least one group ofpullwires. In some embodiments, the load balancing mechanism may includea two-way differential mechanism, which includes a rotating input shaft,at least one pinion coupled to and driven by the rotating input shaft, afirst rotary stage coupled with the at least one pinion and attached toa first of the two pullwires, and a second rotary stage coupled with theat least one pinion and attached to a second of the two pullwires.Rotation of the input shaft results in equal load applied to the twopullwires independent of original lengths of the two pullwires. In otherembodiments, the load balancing mechanism may include a two-waywhiffletree.

At least some of these aspects and embodiments are described in greaterdetail in the following Detailed Description, along with the attacheddrawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrammatic top views of a prior art steerablecatheter, illustrating twisting of the catheter;

FIGS. 2A and 2B are diagrammatic side views of a prior art steerablecatheter, illustrating unwanted proximal bending of the catheter;

FIGS. 3A-3C are diagrammatic side views of a prior art steerablecatheter, illustrating unwanted proximal bending of the catheter;

FIGS. 4A-4C are diagrammatic cross-sectional views of prior artsteerable catheters, illustrating three different configurations forpositioning pullwires in the wall of a catheter;

FIG. 5 is a perspective view of a surgical robotic system, in which anyof the embodiments described herein may be incorporated;

FIGS. 6A-6C are diagrammatic cross-sectional views of a steerablecatheter, illustrating one possible configuration for pullwires atvarious locations along the length of the catheter, according to oneembodiment;

FIGS. 7A and 7B are diagrammatic cross-sectional views of a steerable,nine-pullwire catheter, illustrating one possible configuration forpullwires along a distal articulation section (FIG. 7A) and a proximalshaft section (FIG. 7B) of the catheter, according to one embodiment;

FIG. 7C is a perspective view of a distal portion of the catheter ofFIGS. 7A and 7B;

FIGS. 8A and 8B are diagrammatic cross-sectional views of a steerable,six-pullwire catheter, illustrating one possible configuration forpullwires along a distal articulation section (FIG. 8A) and a proximalshaft section (FIG. 8B) of the catheter, according to one embodiment;

FIGS. 9A and 9B are diagrammatic cross-sectional views of a steerable,six-pullwire catheter, illustrating one possible configuration forpullwires along a distal articulation section (FIG. 9A) and a proximalshaft section (FIG. 9B) of the catheter, according to an alternativeembodiment;

FIGS. 10A and 10B are diagrammatic cross-sectional views of a steerable,eight-pullwire catheter, illustrating one possible configuration forpullwires along a distal articulation section (FIG. 10A) and a proximalshaft section (FIG. 10B) of the catheter, according to one embodiment;

FIGS. 11A and 11B are diagrammatic cross-sectional views of a steerable,eight-pullwire catheter, illustrating one possible configuration forpullwires along a distal articulation section (FIG. 11A) and a proximalshaft section (FIG. 11B) of the catheter, according to an alternativeembodiment;

FIGS. 12A and 12B are diagrammatic cross-sectional views of a steerable,twelve-pullwire catheter, illustrating one possible configuration forpullwires along a distal articulation section (FIG. 12A) and a proximalshaft section (FIG. 12B) of the catheter, according to one embodiment;

FIG. 13 is a chart, illustrating forces applied to a catheter bypullwires, according to one embodiment;

FIGS. 14A and 14B are diagrammatic cross-sectional views of a steerable,twelve-pullwire catheter, illustrating one possible configuration forpullwires along a distal articulation section (FIG. 14A) and a proximalshaft section (FIG. 14B) of the catheter, according to an alternativeembodiment;

FIGS. 15A and 15B are diagrammatic representations of a steerablecatheter embodiment being deformed due to tortuous anatomy; alsoillustrated is the changing tension and slack experienced by thepullwires as a result;

FIGS. 16A and 16B are diagrammatic illustrations of a two-waywhiffletree load balancing mechanism, according to one embodiment;

FIG. 17 is a perspective view of a load balancing mechanism including aspool and a continuous pullwire, according to one embodiment;

FIGS. 18A and 18B are diagrammatic illustrations of a three-waywhiffletree load balancing mechanism, according to one embodiment;

FIG. 19 is a diagrammatic illustration of another three-way whiffletreeload balancing mechanism;

FIGS. 20A-20D are perspective views of a disc-based load balancingmechanism, illustrated in different positions, according to oneembodiment;

FIG. 21 is a perspective view of the disc-based load balancing mechanismof FIGS. 20A-20D, coupled with a pulley;

FIG. 22 is an exploded view of a two-way differential for balancingpullwire tension in a catheter, according to one embodiment;

FIGS. 23A-23C are perspective views of the two-way differential of FIG.17, illustrating three different tension balancing scenarios;

FIGS. 24A-24C are partial side views of the two-way differential of FIG.17, illustrating three different tension balancing scenarios;

FIG. 25 is a perspective views of a splayer coupled with three two-waydifferentials, according to one embodiment;

FIG. 26 is a perspective views of a splayer coupled with four two-waydifferentials, according to one embodiment;

FIGS. 27A and 27B are perspective and side views, respectively, of athree-way differential for balancing tension in pullwires of a catheter,according to one embodiment;

FIG. 27C is an exploded view of the three-way differential of FIGS. 27Aand 27B;

FIG. 27D is a side, cross-sectional view of the three-way differentialof FIGS. 27A and 27B, from the perspective indicated by dotted line “B”in FIG. 27B;

FIGS. 27E and 27F are top, cross-sectional views of the three-waydifferential of FIGS. 27A and 27B, from the perspective indicated bydotted line “A” in FIG. 27B;

FIGS. 27G and 27H are partial side views of the three-way differentialof FIGS. 27A and 27B;

FIG. 28 is a side, cross-sectional view of a distal portion of apullwire catheter;

FIGS. 29A-29C are diagrammatic cross-sectional views of a multi-bend,twelve-pullwire catheter, illustrating one possible configuration forpullwires along a distal articulation section (FIG. 29A), a proximalarticulation section (FIG. 29B), and a proximal shaft section (FIG. 29C)of the catheter, according to one embodiment;

FIGS. 30A and 30B are diagrammatic cross-sectional views of amulti-bend, six-pullwire catheter, illustrating one possibleconfiguration for pullwires along a distal articulation section (FIG.30A) and a proximal articulation section (FIG. 30B), according to oneembodiment;

FIGS. 31A and 31B are diagrammatic side views of a multi-bend catheterin a straight configuration (FIG. 31A) and a double-bend configuration(FIG. 31B), according to one embodiment;

FIGS. 32A-32C are diagrammatic cross-sectional views of a multi-bend,six-pullwire catheter, illustrating one possible configuration forpullwires along a distal articulation section (FIG. 32A), a proximalarticulation section (FIG. 32B), and a shaft section (FIG. 32C),according to one embodiment; and

FIGS. 33A-33C are diagrammatic cross-sectional views of a multi-bend,six-pullwire catheter, illustrating one possible configuration forpullwires along a distal articulation section (FIG. 33A), a proximalarticulation section (FIG. 33B), and a shaft section (FIG. 33C),according to an alternative embodiment.

DETAILED DESCRIPTION

Referring now to the drawings, illustrative embodiments are shown indetail. Although the drawings represent the embodiments, the drawingsare not necessarily to scale, and certain features may be exaggerated tobetter illustrate and explain an innovative aspect of an embodiment.Further, the embodiments described herein are not intended to beexhaustive or otherwise limit or restrict the invention to the preciseform and configuration shown in the drawings and disclosed in thefollowing detailed description.

To address at least some of the challenges with steerable cathetersdiscussed above, a number of embodiments of a “polyrail” catheter willbe described in detail below. In general, these embodiments includemultiple pullwires (also referred to as “control wires,” or simply,“wires”), which are spaced around a circumference of a catheter along aproximal portion of the catheter shaft and then converge toward oneanother so that they are touching or immediately adjacent one anotheralong a distal, articulating portion (i.e., a distal tip) of thecatheter. The embodiments typically include at least one set of at leasttwo pullwires, but they may optionally include multiple sets of two ormore pullwires. One embodiment, for example, may include three sets ofthree pullwires each.

In various embodiments provided herein, a steerable catheter is providedhaving a catheter shaft (i.e., body) formed of sidewalls. The actualshaft or body of the catheter typically runs the entire length of thecatheter and includes one or more articulation sections and a proximal,non-articulating section. In this application, the terms “shaft section”and “shaft” are sometimes used to refer to the proximal portion of thecatheter shaft that does not articulate, in contrast to the more distalportion (or portions) of the catheter shaft that does (or do)articulate.

Various exemplary embodiments may be used as part of a robotic cathetermanipulation system as described below, but the invention is not limitedto use in robotic systems. Several exemplary embodiments are describedbelow in further detail, but these embodiments are only examples andshould not be interpreted as limiting the scope of the invention as setforth in the claims.

Referring to FIG. 5, one embodiment of a robotically controlled surgicalsystem 300 is illustrated. System 300 may include a robotic catheterassembly 302, having a first or outer steerable complement, otherwisereferred to as a robotic sheath or sheath instrument 304 (also referredto simply as a “sheath”) and/or a second or inner steerable component,otherwise referred to as a robotic catheter, guide or catheterinstrument 306 (also referred to simply as a “catheter”). Catheterassembly 302 is controllable using a robotic instrument driver 308.During use, a patient is positioned on an operating table or surgicalbed 310, to which robotic instrument driver 308 may be coupled ormounted. In the illustrated example, system 300 includes an operatorworkstation 312, an electronics rack 314 and an associated bedsideelectronics box (not shown), a setup joint mounting brace 316, andinstrument driver 308. A physician (or “operator”) sits at operatorworkstation 312 and can monitor the surgical procedure and patientvitals and control one or more catheter devices. Operator workstation312 may include a computer monitor to display a three dimensionalobject, such as a catheter instrument or component thereof, e.g., aguidewire and/or a catheter sheath. In some cases, the catheterinstrument may be displayed within, or relative to, a body cavity, organor portion of an organ, e.g., a chamber of a patient's heart. In oneexample, the operator uses a computer mouse to move a control pointaround the display to control the position of the catheter instrument.

System components may be coupled together via cables or other suitableconnectors 318 to provide for data communication. In some embodiments,one or more components may be equipped with wireless communicationcomponents to reduce or eliminate cables 318. Communication betweencomponents may also be implemented over a network or over the Internet.In this manner, a surgeon or other operator may control a surgicalinstrument while being located away from or remotely from radiationsources (e.g., behind a shield or partition), thereby decreasingradiation exposure. With the option for wireless or networked operation,the surgeon may even be located remotely from the patient in a differentroom or building.

I. Localization of Forces and Distribution of Forces—Multi-DirectionalSingle-Bend Catheters

Referring to FIGS. 6A-6C, cross-sectional, diagrammatic views of oneembodiment of a polyrail catheter 20 are illustrated. FIG. 6Aillustrates a cross-section of a catheter 20 having a sidewall 22 andthree pullwires 24, taken from a distal articulation section (i.e.,distal tip) of the catheter 20. Again, this figure is diagrammatic innature, as is evident by the fact that the pullwires 24 are shownresting on the outer surface of the sidewall 22, whereas typically theyare integrated into the sidewall 22. This simplified representation ofthe pullwires and sidewall is used in FIGS. 6A-6C and in many subsequentfigures described below, for simplicity and ease of understanding.Although pullwires are shown on the exterior/outer surface of thesidewalls in these figures, in actual catheter devices described herein,the pullwires will typically (though not necessarily) be located withinthe sidewall of a given catheter embodiment.

The exemplary embodiment of FIGS. 6A-6C includes only three pullwires 24and is unidirectional—i.e., articulates in only one direction. Thissimple example is used here for ease of explanation. FIG. 6B is across-sectional view at a middle divergence section of the catheter 20,and FIG. 6C is a cross-sectional view of a more proximal shaft section.This embodiment circumferentially distributes the strain from pullwiretension in the shaft section (FIG. 6C) through a circumferentiallyspaced placement of the control wires, and then localizes the strain inthe articulation section (FIG. 6A). This isolates the proximal shaftsection from bending deflection during articulation, without requiring astiffness gradient along the length of the catheter 20. This creates amore free and open design space, where the catheter stiffness andmechanical properties can be optimized for specific clinicalrequirements, rather than engineering requirements. Articulation loadlocalization and shaft load distribution can be achieved by usingmultiple pullwires 24 for one articulation direction, which arecircumferentially grouped together in the articulation section (FIG. 6A)and circumferentially distributed in the shaft section (FIG. 6C).Tension applied equally to each pullwire 24 results in a bending momentin the articulation section, while the non-articulating shaft section ofthe catheter is unaffected.

Again, the cross-sectional views of FIGS. 6A-6C illustrate a three-wireexample, with a single articulation direction. In the articulationsection (FIG. 6A), all the pullwires 24 are concentrated toward oneside, so there is a net bending moment pointing toward the 12 o'clockdirection. The magnitude of the bending moment depends on the diameterof the catheter sidewall 22, the distance of the pullwire from theneutral axis and/or the articulation force. In the divergence section(FIG. 6B) of the catheter 20, the pullwires 24 are more distributed butstill symmetrical around the 12 o'clock articulation direction. As thepullwires 24 diverge in the divergence section, each of the pullwires 24creates the same magnitude of bending moment as it did in thearticulation section, but the bending moments are now applied indifferent directions, as shown. Since the pullwires 24 are moredistributed but symmetrical around the articulation direction, thecomponents of the bending moment from each of the outside two pullwires24, which are not in the direction of bending, cancel each other. Thus,there is still a resultant bending moment to the 12 o'clock position,but not as large as in the articulation section.

The pullwires 24 are equally spaced in the proximal shaft section (FIG.6C), and if equal load is applied to each of the three pullwires 24, theoverall combined bending moment is zero. At this point, each pullwire 24creates its own bending moment, but because the pullwires 24 areuniformly distributed, the net result is zero. Thus, there is no bendingmoment along the length of the proximal shaft section. The symmetricdistribution of forces results in a reduction in shaft muscling. Thissymmetric distribution of forces means that stiffening the cathetershaft is not necessary to reduce unwanted bending or muscling. Theadvantage of this design is that the articulation section can be fullydefined, meaning completely isolated from the proximal shaft section,without changing the stiffness of either section. The shaft section canremain flexible, such that tracking performance is enhanced andpotential trauma to the patient's body is minimized. Using multiplepullwires 24 per articulation direction also increases the effectivetensile strength of that direction, enabling the reduction of wirediameter and resulting in overall catheter wall thickness reduction,without compromising safety or risking pullwire failure.

While some catheter embodiments include pullwires that are uniformlyspaced in the catheter shaft section, it is not necessary to haveuniform distribution, if there are more than two pullwires per group.With two pullwires per group, the wires are preferably 180° apart (i.e.,opposite each other) in the shaft, and an equal load should be appliedto both wires to ensure load balancing and no bending moment. However,if there are three or more wires per group, the spaced pullwires of theshaft section may not be equally distributed around the circumference.Rather, in some embodiments, the pullwires are spaced around thecircumference in a non-equal distribution. The minimum requirement forsuch an arrangement is that each pullwire is positioned less than 180°away from its two adjacent pullwires (i.e., the pullwires immediately toits left and right). In such embodiments, any applied load must beproportionally distributed among the pullwires, based on the spacing, toensure the load is distributed evenly. This will be explained furtherbelow.

To achieve an omnidirectional articulation section (i.e., anarticulation section able to articulate in all directions), at leastthree groups of pullwires are employed in some embodiments. In someembodiments, for example, each group of pullwires includes threepullwires, which are redistributed in the shaft section to allow forequal load distribution around the circumference of the shaft section.With three pullwires per group and three groups of pullwires, such anomnidirectional catheter embodiment includes nine pullwires. In otherembodiments, any suitable number and arrangement of pullwires may beprovided.

While the exact pullwire arrangement may vary, each of the cathetersdescribed herein includes an articulation section, a divergence section,and a shaft section. The articulation section includes one or more“articulation sets” of pullwires. Each articulation set is formed ofmultiple pullwires clustered together. As used herein, “clusteredtogether” may mean the pullwires are touching, almost touching,positioned closer to each other than to any other pullwires, or aresimply adjacent/neighboring pullwires. When some of or all the pullwiresin a given articulation set are tensioned, the articulation sectionexperiences a bending moment in the direction of that set. Inomni-directional embodiments, the articulation section of the catheterincludes at least three articulation sets of pullwires. If some or allpullwires in a first articulation set are tensioned while no otherpullwires are tensioned, the articulation section will experience abending moment in the direction of the first articulation set. If anequal amount of tension is applied to pullwires in a first articulationset and to pullwires in an adjacent second articulation set, thearticulation section will experience a bending moment in a directionhalf way between the first and second articulation sets. The tensionforces applied to one or more articulation sets may be adjusted in orderto achieve articulation in any desired direction.

In the shaft section, the pullwires are arranged so as to minimize oreliminate bending moments and resultant compression and torsionalforces. That is, the pullwires that formed a given articulation set inthe articulation section are substantially distributed around thecircumference of the catheter in the shaft section, in order todistribute loads. In some embodiments, the pullwires forming anarticulation set are equally distributed around the circumference of thecatheter by the time they reach the shaft section. In some embodiments,the pullwires of the shaft section are grouped into multiple “shaftsets.” In at least some such embodiments, no pullwires found together ina given articulation set are found together in any given shaft set. Thatis, the arrangement of pullwires is changed to form different groupingsbetween the articulation section and the shaft section. The pullwiresare rearranged into different groupings, so that a tension applied toone articulation set can cause a bending moment in one direction in thearticulation section while that same tension can be distributed equallyaround the circumference of the shaft section (so that the forces in theshaft section cancel each other and no bending moment is experienced inthe shaft section).

Between the articulation section and the shaft section is a divergencesection in which the positions of the pullwires transition from thearrangement of the articulation sets to the arrangement of the shaftsets. Any suitable means of transitioning may be used. In someembodiments, at least some of the pullwires overlap one another in thedivergence section, in order to transition from their distalcircumferential positions in the articulation section to their proximalcircumferential positions in the shaft section.

Referring now to FIGS. 7A and 7B, cross-sectional, diagrammatic views ofone embodiment of an omnidirectional, nine-wire catheter 30 are shown.FIG. 7C is a perspective view of a distal portion of the same catheter30, illustrating the articulation section 36A, the divergence section36B, and a distal portion of the shaft section 36C. The catheter 30includes a catheter sidewall 32 and three groups of pullwires 34, whereeach group of pullwires 34 is numbered 1, 2, or 3. In describing thisembodiment, the pullwires 34 will be described as belonging to group 1,2, or 3, and individual pullwires 34 will be described as “pullwire 1a,” “pullwire 2 b,” and the like. The groups of pullwires 34 may also bereferred to, for example, as “articulation set 1” (pullwires 1 a-1 c),“articulation set 2” (pullwires 2 a-2 c), and “articulation set 3”(pullwires 3 a-3 c). The groups of pullwires 34 may also be referred toas “shaft set 1” (pullwires 3 c, 1 b, 2 a), “shaft set 2” (pullwires 1c, 2 b, 3 a), and “shaft set 3” (pullwires 1 a, 3 b, 2 c).

FIG. 7A is a view taken along the articulation section 36A (or “distalsection” or “tip”) of the catheter 30, and FIG. 7B is a view taken alongthe shaft section 36C (or “proximal shaft”) of the catheter 30. Thenumbered pullwires 34 of each group are anchored close together in thearticulation section 36A (FIG. 7A), to concentrate or localize theforces in respective isolated areas. In the shaft section 36C (FIG. 7B),the numbered pullwires 34 of each group have diverged and formed newgroupings with each of the new groupings having one pullwire 34 fromeach of the respective numbered groups. This may be referred to as a“polyrail” design, because the shaft load is distributed on multiple“rails.”

In the embodiment depicted in FIGS. 7A-7C, one pullwire 34 from eachnumbered grouping continues straight from the articulation section downto the shaft section. In FIGS. 7A and 7B, those are the pullwires 34lettered “b” (i.e., 1 b, 2 b, and 3 b). Adjacent pullwires 34, labeled“a” and “c”, are switched in the transition from articulation sectiongroupings to shaft section groupings, pullwire 1 a switches positionswith 3 c, 2 a switches positions with 1 c, and 3 a switches positionswith 2 c. In terms of clock position, pullwire 1 b has stayed in the 12o'clock position, 1 c has been spiraled clockwise on or within thesidewall 32 to the 4 o'clock position, while pullwire 1 a has spiraledcounter clockwise on or within the sidewall 32 to the 8 o'clockposition. Likewise, pullwire 2 a has moved to the 12 o'clock position,pullwire 2 c has spiraled to the 8 o'clock position, pullwire 3 c hasmoved to the 12 o'clock position, and pullwire 3 a has spiraled to the 4o'clock position.

If articulation in the 12 o'clock position is desired, pullwire group 1(or “articulation set 1”) will have equal force applied to all threepullwires 34. This results in a net bending moment in the 12 o-clockposition in the articulation section, causing the tip to bend toward the12 o'clock position. For example, if a load of approximately 15N wererequired to bend the distal tip of the catheter 30 to a desired angle, aload of 5N would be placed on each of the pullwires 34 in the grouplabeled 1 a-1 c, and no load would be applied to the pullwires 34 in thegroups labeled 2 a-2 c and 3 a-3 c. In other words, in the articulationsection 36A, 15N is applied at 12 o'clock, 0N is applied at 4 o'clock,and 0N is applied at 8 o'clock. In the shaft section 36C, however, 5Nwill be applied at 12 o'clock, 5N will be applied at 4 o'clock and 5Nwill be applied at 8 o'clock. Therefore, there will be no net bendingmoment in the shaft section 36C, because there is equal force beingapplied over equally spaced wires.

Although the examples illustrated in FIGS. 6A-6C and 7A-7C include threepullwires per group, the minimum number of pullwires necessary toachieve shaft load distribution and articulation load localization istwo wires per group. Therefore, some embodiments may include as few assix pullwires, while still remaining omnidirectional.

FIGS. 8A and 8B are cross-sectional, diagrammatic views of oneembodiment of an omnidirectional catheter 40 that includes a cathetersidewall 42 and six pullwires 44. As in FIGS. 7A and 7B, the pullwires44 in this catheter 40 are labeled in groups by a number (numbers 1-3),and pullwires 44 within a group are differentiated by letter (letter “a”or “b”). In this embodiment, pullwires 1 a and 1 b are adjacent to eachother in the articulation section (FIG. 8A) and opposite each other inthe shaft section (FIG. 8B). Likewise, pullwires 2 a and 2 b areadjacent to each other in the articulation section and opposite eachother in the shaft section. The same is true of pullwires 3 a and 3 b.Thus, if tension is applied only to pullwire group 1, for example, ifpullwires 1 a and 1 b are equally tensioned, the articulation sectionwill experience articulation in the 12 o'clock direction.

Referring now to FIGS. 9A and 9B, an alternative embodiment of asix-pullwire, omnidirectional catheter 50 is illustrated incross-section, again having six pullwires 54 and a catheter sidewall 52.In this embodiment, the pullwires 54 have the same configuration alongthe proximal shaft section (FIG. 9B) as they did in FIG. 8B. Along thearticulation/tip section (FIG. 9A), however, the two pullwires 54 ineach group (groups 1-3) come together to touch or nearly touch oneanother. Thus, in various embodiments, pullwires said to be grouped orclustered together in the articulation section may be touching, nearlytouching, positioned closer to each other than to any other pullwires,or simply located in adjacent positions. The same is true for pullwiresgrouped or clustered together in the shaft section.

As described above, some embodiments of “polyrail” catheters may includethree groups of pullwires, to achieve omnidirectional articulation ofthe catheter tip without rotating the shaft. In alternative embodiments,however, polyrail catheters may include four or more groups ofpullwires. Alternatively, some embodiments may include two groups, oreven just one group, of pullwires, for example in embodiments where itis not required to have omnidirectional articulation or where it ispossible to rotate the catheter tip via other means.

FIGS. 10A and 10B illustrate one embodiment of a polyrail catheter 60,having a catheter sidewall 62 and four groups of two pullwires 64. Eachof the two pullwires 64 clustered within a group (e.g., located next toone another) along the articulation section (FIG. 10A) are locatedacross the shaft 62 from one another along the shaft section (FIG. 10B).

FIGS. 11A and 11B illustrate an alternative embodiment of a polyrailcatheter 70, having a catheter sidewall 72 and four groups of twopullwires 74. In this embodiment, the two pullwires 74 clusteredtogether within an articulation section group are located across theshaft 72 from one another along the shaft section (FIG. 11B), as in FIG.10B. In this embodiment, however, the configuration of the articulationsection (FIG. 11A) is different. In the articulation section, the twopullwires 74 of each articulation section group are located farther fromone another than they were in the articulation section of FIG. 10A. Inother words, the pullwires 74 of each group in the articulation sectionare separate from one another and not touching one another.

FIGS. 12A and 12B illustrate yet another alternative embodiment of apolyrail catheter 80, having a catheter sidewall 82 and four groups ofthree pullwires 84 each (twelve pullwires 84 in total). In thisembodiment, the three pullwires 84 within an articulation section groupare located next to one another along the articulation section (FIG.12A) and are significantly distributed from one another along the shaftsection (FIG. 12B). In some embodiments, the three pullwires 84 of anarticulation section group are equally distributed around thecircumference of the catheter 80 in the shaft section, such that thereare 120 degrees between each pullwire of the group.

The three pullwires 84 within an articulation section group do notnecessarily need to be uniformly positioned within the shaft section.Although some embodiments include a uniform distribution, sometimes auniform distribution may not be possible, due to the position of otherpullwires, as shown in FIG. 12B. In such embodiments, the pullwires ofan articulation section group are widely distributed within the shaftsection, and the load placed on each pullwire is adjusted based on itsangular position, to achieve equal load distribution around the shaftsection.

Referring now to FIG. 13, an equation that relates the load on eachpullwire (1 a, 1 b, 1 c) to its angular position on the circumference ofthe shaft section of a catheter 320 will now be described. For ease ofreference, pullwire 1 b is positioned at 12 o'clock, and the other twopullwires 1 a, 1 c are positioned α degrees to either side of pullwire 1b. The overall force applied to the catheter 320 is F. This force isdivided among all three pullwires. The force on pullwire 1 b is labeledF1, and the force on pullwire 1 a and pullwire 1 c is labelled F2. Ifα=120 degrees, and F=15N, then the force of 15N is applied equally onthe three pullwires (F1 and F2=5N), to ensure no bending moment in theshaft.

When three pullwires are present, if α=90 degrees or less, then thedesign does not work. It is not possible to distribute the forcesuniformly in the shaft. α must be greater than 90 degrees for the loadto be adequately distributed in the shaft section. α cannot be greaterthan 180 degrees in the embodiment shown, because then pullwire 1 abecomes pullwire 1 c, and pullwire 1 c becomes pullwire 1 a. Therelationship between F1 and F2 for all three pullwires as α goes from 90degrees to 180 degrees is shown diagrammatically in the graph 322 ofFIG. 13. On the left side of the graph 322, F1 is zero and F2=F/2. Thisis essentially a two-pullwire design. There is no load applied topullwire 1 b, and the load is shared equally between pullwires 1 a and 1c. When α increases to 120 degrees, F2=F1, as shown by the intersectionof the dashed line and the starred line. In such arrangements, there isuniform tension on all pullwires. As α continues to increase towards 180degrees, F2 decreases towards F/4 and F1 increases toward F/2.Therefore, even if all pullwires are not uniformly distributed, butinstead, two pullwires are offset an angle α from the first pullwire 1b, a force may be proportionally applied to each pullwire, such that auniform load is applied to the shaft. The equations for the force F1 tobe applied to pullwire 1 b and for the force F2 to be applied topullwire 1 a and 1 c, in order to uniformly distribute load about thecircumference of the shaft section, are depicted in FIG. 13.

Referring back to FIG. 12B, pullwire 1 b is in the 12 o'clock position,pullwire 1 c is in the 3:30 position, and pullwire 1 a is in the 8:30position. Therefore, there are 105 degrees between pullwires 1 b and 1 cin the shaft section, 105 degrees between pullwires 1 b and 1 a in theshaft section, and 150 degrees between pullwires 1 a and 1 c in theshaft section. Therefore α=105 degrees, and substituting α into theabove described equations, the 15N is distributed and applied asfollows: F2=5.95N on pullwire 1 a, F2=5.958N on pullwire 1 c, andF1=3.084N on pullwire 1 b.

FIGS. 14A and 14B illustrate yet another alternative embodiment of apolyrail catheter 90, having a catheter sidewall 92 and four groups ofthree pullwires 94. In this embodiment, the three pullwires 94 in eacharticulation section group are spaced equidistant from one anotheraround the circumference of the catheter along the shaft section (FIG.14B) and are clustered close to one another (but not touching oneanother) along the articulation section (FIG. 14A).

As described above, the catheter embodiments disclosed in thisapplication generally include a distal articulation section (or“catheter tip,” “distal portion” or other similar terms) and a shaftsection (or “proximal shaft portion” or other similar terms). Thecatheters also typically include a “divergence section” or “transitionsection,” where the pullwires transition from their arrangement alongthe shaft section to their arrangement along the articulation section.The location of the transition identifies the transition between theshaft and the articulation section of the catheter. This may vary alongthe catheter. The length of the transition or divergence section mayalso vary. Typical articulating catheters have a relatively shortarticulation section, compared to the overall length of the catheter.Thus, a typical transition section is located close to the distal end ofthe catheter. Alternatively, however, the transition section may bepositioned at any location along the catheter length, since the lengthsof the shaft and the articulation section may also vary between designs.Some embodiments may even include multiple transition sections along thecatheter length, as will be described further below.

Referring again to FIGS. 2A and 2B, a straight catheter is shown withthe dashed outline. When a steering wire (i.e., pullwire or controlwire) is pulled, a traditional catheter 10, with a soft trackable shaft,would deflect, as shown in FIG. 2A. A traditional catheter 10 with astiff shaft is shown in FIG. 2B. The embodiment in FIG. 2B wouldgenerally be preferred, from an articulation perspective, because itproduces predictable articulation. A catheter 10 with a stiff shaft,however, will not track through tortuous anatomy. An articulation shapelike the one illustrated in FIG. 2B, however, is achievable with thepolyrail catheters described herein, even with a soft, flexible, andtrackable shaft.

In addition to eliminating unwanted shaft deflection, the polyrailcatheter embodiments described herein isolate the articulation sectionwithout varying stiffness. Traditional catheter designs identify thearticulation section from the shaft by making the articulation sectionsoft and the shaft section stiffer. The polyrail catheter allowsarchitectures to be better optimized for other performance properties,such as tracking, push-ability and reaching clinical targets.

The polyrail design ensures that the group of pullwires required toarticulate the articulation section of the catheter in one direction issignificantly distributed around the catheter shaft section, to ensurethat the shaft does not undergo any unintended bending moment. Asdescribed above, preventing any unintended bending moment requires thatan equal force (or a force proportionate to the spacing of non-equallyspaced pullwires) be applied to each of the pullwires. One design foraccomplishing the application of equal force is to attach all pullwiresfrom one group to the same pulley in the splayer. In other words, insuch an embodiment, each group of pullwires is attached at or near oneanchor point at the distal end of the catheter, then they diverge to bewidely distributed around the catheter in the shaft section, and thenthey converge to one anchored location at the proximal end at thepulley.

While this design works well if the entire shaft is held straight, itmay not work well when the catheter is bent. For a bent catheter, anypullwires positioned in lumens on the inside of the bend will becompressed and have excess slack, whereas any pullwires in lumens on theoutside of the catheter will be stretched and have increased tension.Therefore, if all pullwires are attached to one pulley and anarticulation command is initiated, the pullwire(s) on the outside of thebend will take more of the load than the pullwire(s) on the inside,because the outside pullwires have a higher initial tension. If thepullwires spread around the shaft do not take an equal (orspacing-proportionate) load, then this design will not work as intended.

II. Interface Design for Manipulating Pullwires

It is important that each pullwire within a set of pullwires have theintended force applied to it, such that the force is truly distributedin the shaft as articulation is commanded. This is especially importantas the catheter is put into different tortuosity and bends. As thecatheter is put into a bend, the material on the inside of the catheterwill compress (shorten) and the material on the outside of the bend willstretch (lengthen). However, the length of the pullwires will remainunchanged, because they are floating (i.e., unconstrained) within thewalls of the catheter. That is, rather than compressing or stretching,the pullwires will slide further into, or partially out of, the proximalend of the catheter. Since the proximal end of each pullwire remainsattached to a pulley or other control means, this sliding results inslack along the pullwires on the inside of the bend and additionaltension on the pullwires on the outside of the bend. For example, if theshaft section of the catheter shown in FIGS. 11A and 11B were benttowards the 12 o'clock direction, the tension on pullwires 4 b and 2 awould decrease, and the tension on pullwires 4 a and 2 b would increase.

FIGS. 15A and 15B represent the above-described phenomenondiagrammatically. A catheter 100 with a shaft 102 and two pullwires 103,104 is illustrated. When the shaft section of the catheter 100 is bent,as in FIG. 15B, a first pullwire 103 tends to slide inward (by ΔL) whileremaining attached to a pulley or other attachment point at a proximalend (not shown), and thus, will experience increased tension. A secondpullwire 104 tends to slide outward (by ΔL) while remaining attached toa pulley or other attachment point at a proximal end (not shown), andthus, experiences decreased tension or slack.

A. Multiple Pulley and Shared Pulley Embodiments

One way to account for the need for an equal amount of tension (or acarefully controlled amount of tension) on multiple pullwires is byhaving each pullwire fixed to its own pulley assembly, containing apulley, torque sensor, and motor. Such an embodiment allows torquesensors to measure the load on each pullwire in a set and adjust theangular displacement of the pulley, such that the force on all pullwireswithin the set is equal to a commanded force. In such embodiments, the6, 8, 9, and 12-wire designs require 6, 8, 9, and 12 pulley assemblies,respectively. Ideally, however, a catheter design would not require sucha large number of pulley assemblies, due to the complexity, weight andsize of an instrument driver having so many pulleys. For example, aninstrument driver of a surgical robotic system will have a limitednumber of motors for driving such pulley assemblies, due to sizeconstraints on the instrument driver at a patient's bedside. To reducethe number of motors required by the robotic system, an alternativeactuation method may be implemented.

One simple actuation method used in some embodiments involves fixingeach pullwire in a group to the same pulley. Doing this requires thepullwires to either be made of an elastic material or have elasticityadded, for example by attaching an extension or torsion spring in serieswith it. Without an elastic pullwire, when the first pullwire within agroup initially has tension applied to it, it will have to elongate anamount equal to the amount of slack in the loosest pullwire in the groupbefore both pullwires are applying load. If a pullwire has an effectivespring constant of k, and the amount of slack in the loosest pullwirewhen the first pullwire is initially tensioned is equal to ΔL, then thedifference in force between the two pullwires will be ΔL*k. Given themodulus of elasticity for a typical high-tensile pullwire, the firstpullwire may break before the other pullwires in the group gain tension,and if it does not break, there will be a large difference in forcebetween the pullwires. This will result in an unequal load distributionaround the circumference and suboptimal polyrail performance.

If a low enough k value for the pullwire is chosen by using pullwireswith high elasticity, the issue of unequal load distribution is reduced,however possibly at the cost of tensile strength. Rather than usingelastic wires as pullwires, an extension spring may be soldered, welded,or fixed to the proximal end of each pullwire, such that a high tensilewire can be used for tensile strength and a very low k value can stillbe achieved.

B. Whiffletree Embodiments

In some embodiments, another actuation method can be implemented in theform of a load balancing mechanism. Referring now to FIGS. 16A and 16B,in one embodiment, a load balancing mechanism in the form of a two-waywhiffletree 110 may be employed. This two-way whiffletree 110 isillustrated diagrammatically in FIG. 16A. This mechanism may be used todistribute the forces in any polyrail catheter embodiment that includestwo pullwires per pullwire group (for example, the embodimentsillustrated in FIGS. 8A-11B). This is done by fixing the two pullwiresin a group to opposite ends of a rod with a third wire fixed at thecenter of the rod extending to the pulley. A free body diagram is shownin FIG. 16A, where the upward pointing arrows 111, 112 represent thetensioned pullwires going into the catheter, and the downward pointingarrow 113 represents the wire fixed to a pulley or linear actuator.Points (A), (B) and (C) are free to pivot, such that when a pullwirepath length changes, the rod rotates about point (B) to compensate, asshown in FIG. 16B. If equal force is desired on each pullwire, it isimportant that point (B) be located an equal distance away from point(A) and point (C). If it is preferred that one pullwire have more loadapplied to it, however, then point (B) should be located closer to thatpullwire. This would be the case, for example, with a three-waywhiffletree used for a polyrail embodiment including three pullwires perset (for example, the embodiments in FIGS. 7A-7C, 12A-12B and 14A-14B).

Referring now to FIG. 17, an alternative embodiment for a load balancingmechanism 114 is illustrated diagrammatically. Load balancing mechanism114 may include a spool 115 (or “disc”) and a continuous pullwire 116that is one piece but acts as two pullwires. Load balancing mechanism114 may be used to distribute the forces in any polyrail catheterembodiment that includes two pullwires per pullwire group. The twopullwires of each group may actually take the form of the one continuouspullwire 116, looped around spool 115. Alternatively, two individualpullwires may be attached together and looped around spool 115. Spool115 is configured such that it may be pulled by the pulley in thesplayer (not shown in FIG. 17). As tension increases when the pulley isrotated, spool 115 may rotate such that both ends of continuous pullwire116 have equal tension.

Referring now to FIGS. 18A, 18B, and 19, a three-way whiffletree 120 mayinclude two whiffletrees—one unbiased (i.e., balanced) whiffletree 122,as in FIGS. 16A and 16B, and one biased whiffletree 124. FIGS. 16A and16B depict a free body diagram of the three-way whiffletree 120. FIG. 16is a front view of one embodiment of a three-way whiffletree assembly120, which includes two rods 126A, 126B attached to five wires128A-128E.

Wires 128B, 128E, and 128D represent pullwires in the catheter and arefixed at locations F, A, and C, such that they can pivot about theirfixed locations. Force is applied to the entire assembly 120 at locationE. A wire or linkage 128C also extends between locations B and D and canpivot about those points as well. When location E is actuated, theassembly 120 will adjust itself, such that loads applied to pullwires128B, 128E, and 128D at locations F, A, and C are equal. Pullwires 128Eand 128D at locations A and C are equal, because they are a part of theunbiased whiffletree 122 (location B is the same distance from point Aas from point C). Pullwire 128B and linkage 128C at locations F and Dare a part of the biased whiffletree 124 and have unequal load appliedto them, because point E is closer to point D than to point F. If thedistance between point E and D is half of the distance between point Fand point E, then the wire/linkage 128C fixed at point D has twice theleverage as the pullwire 128B at point F. This balances the load fromthe unbiased whiffletree, with load applied at point F.

The loads applied at points F, A, and C do not need to be split equallyeither. For example, if the pullwires in a group of the nine-wire designof FIGS. 7A-7C are not equally spaced, the whiffletree could be designedsuch that the load is still equally distributed. If instead of pullwires1 a and 1 c being located 120 degrees from pullwire 1 b in the shaft,they are 100 degrees apart, and load is still equally applied to allthree, there will be unwanted shaft deflection in the 12 o'clockdirection. To solve this, the whiffletree of some embodiments is biased,such that pullwires 1 a and 1 c are fixed at points A and C, and point Eis located such that point F receives slightly more load (E is movedcloser to F than depicted in FIGS. 18A and 18B but still not closer thanpoint E to D). The non-uniform distribution of the pullwires within eachgroup in FIG. 12B would also require a similar whiffletree design suchthat a non-uniform load is applied to each pullwire so that the overallload is still equally distributed on the shaft.

Referring now to FIGS. 20A-20D, another alternative embodiment of athree-way load balancing mechanism 230 is illustrated diagrammatically.The illustrated mechanism 230 may include a disc 232, coupled with threepullwires 234, and it may be used to distribute the forces in anypolyrail catheter embodiment that includes three pullwires 234 perpullwire group. The three pullwires 234 may be attached at differentpoints near the circumference of the disc 232. If all three pullwires234 are equal length, then the disc 232 will be maintained in a straightconfiguration, as shown in FIG. 20A. If the pullwires 234 becomeunbalanced, then the disc 232 tilts or pivots about its central axis tocompensate and balance the load.

Referring to FIG. 21, the center of the disc 232 is attached to a pulley238 in the splayer via a wire 236, for example. As tension increaseswith rotation of the pulley, the disc 232 may orient (e.g., tilt orpivot) as necessary, such that all three pullwires 234 have equal orintended tension. In embodiments where uniform tension in all threepullwires 234 is desired, it is achieved by putting equal spacing (i.e.,120 degrees) between each pullwire 234 and by placing each pullwire 234an equal radial distance away from the center of the disc 232 (and anequal distance away from the location of the pulley attachment). Similarto the other load balancing designs described above, the load balancingmechanism 230 may also be used even if the pullwires 234 are notintended to be uniformly tensioned. In such embodiments, the desiredrelative load adjustment can be achieved by adjusting the spacing and/orradial location of the pullwires 234 such that the distance between themcompensates for the load to be applied to them.

C. Gear Differential Embodiments

While the whiffletree mechanism just described may be used to distributethe pullwire load in a polyrail catheter design, it might not be idealin all embodiments. In alternative embodiments, therefore, a rotationaldifferential mechanism may be implemented on the pulley within thesplayer of the catheter. A rotational differential mechanism may bepreferred in some embodiments, because the pulley itself can be replacedby it. Additionally, the rotational differential mechanism can bescaled, such that it fits in the same area of the splayer as the pulley.Also, a differential can balance or distribute load over much greaterchanges in shaft deflection, as compared to a whiffletree.

FIG. 22 is an exploded, perspective view of one embodiment of a two-waydifferential mechanism 130. In this embodiment, the differentialmechanism includes an input shaft 132, a stage one 134, a drive shaft136, four pinions 138, four pinion axles 139 and a stage two 140. Theinput shaft 132 of the differential 130 is configured to engage with theoutput shaft of the robotic surgical system or sterile adaptor (notshown here). As the robot commands articulation, the output shaft of therobotic instrument driver rotates and directly results in rotation ofthe input shaft 132. The input shaft 132 is fixed to the drive shaft136. Therefore, when articulation is commanded, the instrument driverrotates the output shaft, which directly results in rotation of theinput shaft 132 and the drive shaft 136. In various embodiments,multiple pinions 138 are provided, which are free to rotate about theiraxes. In this embodiment, there are four pinions 138. Each pinion 138 isconcentric with, and disposed on, a separate axle 139 extendingperpendicularly from the drive shaft 136. Alternative embodiments mayhave as few as one pinion 138 or more than four pinions 138. In thisembodiment, the drive shaft 136 and the axles 139 are all one piece,although in alternative embodiments, the axles 139 may be separatepieces attached to the drive shaft 136. Stage one 134 and stage two 140are cylindrical components, free to rotate around drive shaft 136. Eachstage 134, 140 has one pullwire fixed to it (not shown). The pullwiresextend from the catheter. Each stage 134, 140 also includes a bevel gear135, which is driven by the bevel on the pinions 138.

FIGS. 23A-23C illustrate how the differential 130 may operate to balanceforces equally, independent of the path length of two pullwires 142,144. A first pullwire 142 is attached to stage one 134, and a secondpullwire 144 is attached to stage two 140. Each figure shows thedifferential 130 before (left hand side) and after (right hand side)tension is applied to the pullwires 142, 144 by the robotic instrumentdriver. On the left side of FIG. 23A, for example, both pullwires 142,144 have equal slack. Therefore, as the drive shaft 136 is rotated, thepinions 138 do not rotate, and stage one 134 and stage two 140 rotatetogether until all the slack is taken up and tension is applied to thepullwires 142, 144 (left hand side of FIG. 23A). Then, as the driveshaft 136 continues to rotate and tension is applied, the force is splitequally between the two pullwires 142, 144 (right hand side of FIG.23A).

In FIG. 23B, the first pullwire 142, fixed to stage one 134, has moreslack than the second pullwire 144, fixed to stage two 140. As the driveshaft 136 rotates, this time the pinions 138 rotate (as described inmore detail below), which drives stage one 134 to rotate and take up theslack, while stage two 140 remains stationary. This ensures that thetension on the second pullwire 144, fixed to stage two 140, does notincrease until the tension on the first pullwire 142, fixed to stage one134, is equal to it. Then, when there is uniform tension on bothpullwires 142, 144, the pinions 138 no longer rotate, and stage one 134and stage two 140 rotate with the drive shaft 136.

FIG. 23C illustrates the opposite scenario of FIG. 23B. This time, thereis more slack in the second pullwire 144 than in the first pullwire 142.In such a scenario, the pinions 138 drive stage two 140 to rotate andtake up the slack while stage one 134 remains stationary until thetension in both pullwires 142, 144 is equal.

FIG. 24A shows a partial side view of the differential 130 in the sameconfiguration as illustrated in FIG. 23A, when each of the pullwires142, 144 has equal slack. When there is equal slack, F1 is equal to F2,and thus, the pull on the upper teeth of the pinion 138 to rotate in thecounterclockwise direction is equal and opposite to the pull on thelower teeth of the pinion 138 to rotate in the clockwise direction. Insuch a scenario, each side of a pinion 138 applies equal force to stageone 134 and stage two 140, and the pinion 138 does not rotate about itsaxle. Each of the pinions 138 will rotate with the input shaft anddriver shaft about the central axis of the differential 130.

FIGS. 24B and 24C show partial side views of the differential 130 in thesame configurations as depicted in FIGS. 23B and 23C, respectively. InFIG. 24B, F2 is greater than F1, due to slack on the first pullwire 142attached to stage one 134. Therefore, the pinions 138 rotate in thecounterclockwise direction, thereby taking up the slack. In FIG. 24C, F1is greater than F2, due to slack on the second pullwire 144 attached tostage two 140. Therefore, the pinions 138 rotate in the clockwisedirection to take up the slack. Pinions 138 generally rotate asrequired, to achieve uniform tension on both pullwires 142, 144.

The achievement of uniform tension on both pullwires assumes that eachof the pullwires is attached to stage one 134 and stage two 140 at equaldistances from the central axis. This general gear differential designmay also be used in embodiments where it is desired to apply more forceon one pullwire than the other. In such embodiments, the pullwire thatrequires higher loads should be placed at a proportionally smallerdistance from the central axis than the pullwire requiring smallerloads.

FIGS. 25 and 26 illustrate two different embodiments of a splayer 150,152 coupled with different numbers of differentials 130—splayer 150coupled with three differentials 130 in FIG. 25, and splayer 152 coupledwith four differentials 130 in FIG. 26. A splayer 150, 152 is often usedto attach pullwires to pulleys, so that they can interface with aninstrument driver. Such splayers are described, for example, in U.S.Pat. No. 8,052,636, which is fully incorporated herein by reference.Splayers 150, 152 are often described as interfaces between a roboticcatheter and an instrument driver. Many instrument drivers in use todayare designed to control four pulleys, and hence, four pullwires. Thesplayer 150 illustrated in FIG. 25 may allow six pullwires, and thesplayer 152 illustrated in FIG. 26 may allow eight pullwires, to beattached to the splayer 150, 152 via three or four two-way differentials130.

The differential 130 described above is designed to balance the forcesbetween two pullwires and is thus used in 6-wire or 8-wire embodiments,for example. In catheter embodiments that include nine pullwires, forcesmust be distributed in groups of three wires, and thus a three-waydifferential is needed.

Referring now to FIGS. 27A-27H, one embodiment of a three-waydifferential 160 is illustrated. As shown in the perspective view ofFIG. 27A, the three-way differential 160 is configured to distribute theload applied between three pullwires 161 within a group. FIG. 27B is aside view of the three-way differential 160, showing locations of afirst cross-sectional view (dotted line A, corresponding to FIGS. 27Eand 27F) and a second cross-sectional view (dotted line B, correspondingto FIG. 27D). As shown in the exploded view of FIG. 27C and the side,cross-sectional view of FIG. 27D, the three-way differential 160 mayinclude an input shaft 162 (with three pegs 163), a sun gear 164, threeplanet gears 166, a ring gear 168, a stage one 170, a drive shaft 172(with four pinion axles 173 protruding from it), four bevel pinion gears174, a stage two 176, a stage three 178, and a stage three shaft 179.The differential 160 may operate according to the same principle as thethree-way whiffletree, except rotationally, where one pullwire perarticulation direction is fixed to each of the three stages 170, 176,178. The three-way differential 160 is split up into two, two-waydifferentials—one biased differential and one unbiased differential. Thebiased differential distributes the torque 2-to-1 between the unbiaseddifferential and stage three 178, respectively. The unbiaseddifferential then balances torque equally between stage one 170 andstage two 176. If tension on the three pullwires is not equal, thenstages 170, 176, 178 will rotate relative to each other with the aid ofthe rotating pinions 174, until equal torque in each stage 170, 176, 178is achieved. This results in a balanced equilibrium between the threepullwires, regardless of catheter curvature or manufacturing tolerances.An omnidirectional catheter will typically include three differentials160 total, one for each articulation direction.

The stage three shaft 179 includes a keyed end, which passes through abore in the drive shaft and mates with a central bore in the sun gear164. Similarly, the drive shaft 172 has a keyed end, which passesthrough a bore in the stage one 170 and mates with a central bore in thering gear. Thus, the stage three shaft 179 is driven by the sun gear164, and the drive shaft 172 is driven by the ring gear 164. The pegs163 of the input shaft 162 drive the planet gears 166, which are able tospin about their own axes and also about the central axis of the inputshaft 162.

Referring to FIGS. 27E and 27F, the mechanism of the three-waydifferential will be described. Torque from the input shaft 162 appliesa radial force to the inside of planet gears 166. The planet gears 166mesh with the sun gear 164 and the ring gear 168 and are free to rotateabout their own axes. In some embodiments, the radius of the sun gear164 is half the radius of the ring gear 168. Thus, if the torque of thesun gear 164 is half the torque of the ring gear 168, the resultanttangential force on each side of the planet gear 166 will be equal, asshown in FIG. 27E. Because the tangential forces on the planet gear 166are equal and opposite, the planet gear 166 does not rotate about itsown axis, but rather the axis of the differential 160. The reduction isbiased, such that the ring gear 168 has twice the mechanical advantageas the sun gear 164. Therefore, two pullwires driven by the ring gear168 have equal tension to the one pullwire driven by the sun gear 164.If the torques of the ring gear 168 and the sun gear 164 are notdistributed 2-to-1 respectively (in other words, if the two pullwiresdriven by the ring gear 168 are not applying two times the tension asthe pullwire driven by the sun gear 164 because of shaft curvature), theplanet gears 166 will rotate until equilibrium is achieved.

FIG. 27F shows the planetary gear system in an unbalanced state. Oncethe torque between the sun gear 164 and the ring gear 168 is distributed2-to-1 respectively, torque is applied to the sun gear 164, which isfixed to stage three 178, and the ring gear 168, which will balancestage one 168 and stage two 176 through an unbiased differential.

T_(sun) = r_(sun) * F T_(ring) = r_(ring) * F$F_{sun} = {F_{ring} = {\frac{T_{sun}}{r_{sun}} = \frac{T_{ring}}{r_{ring}}}}$$\frac{T_{sun}}{1} = \frac{T_{ring}}{2}$ T_(ring ) = 2 * T_(sun)

Referring again to FIGS. 27C and 27D, the ring gear 168 is fixed to thedrive shaft 172, which applies a radial force to the bevel pinion gears174 in the unbiased differential. The unbiased differential isessentially the two-way differential shown in FIG. 22, except the torqueis applied from the ring gear 168, rather than the input shaft 162. Theunbiased differential drives two of the three pullwires of anarticulation axis and balances the torques equally between stage one 170and stage two 176.

FIG. 27G shows the unbiased differential balancing forces on stage one170 and stage two 176 equally. Torque from the ring gear 168 applies aforce on the pinion bevel gear 174 until stage one 170 and stage two 176are applying equal force. FIG. 27H is an example of the unbiaseddifferential in an unbalanced state, where the torque of stage two 176is less than the torque of stage one 170. In this case, stage two 176would rotate, while stage one 170 would be kept stationary, until thetorques were balanced.

As described above, in other embodiments, the loads to the two pullwiresare intentionally distributed unequally. In such embodiments, thepullwires are not uniformly positioned within the catheter shaft. Insuch embodiments, a biased differential may be provided by attachingeach of the pullwires at a different radius from the center axis, suchthat the loads are still distributed throughout the shaft and there isno net bending moment.

III. Multi-Bending Catheter Design

In some embodiments, the load distribution mechanisms described abovemay be used in a double-bending catheter or multi-bending catheter. Amulti-bending catheter includes a catheter body having a proximalnon-articulating shaft section and two or more distal articulationsections. The articulation sections are aligned along the catheter bodywith one or more articulation sections being more distally locatedrelative to one or more other articulation sections. Accordingly,“distal articulation sections” and “proximal articulation sections” arereferred to herein; however, in general, each of these articulationsections is distal to the proximal non-articulating shaft section. Thearticulation sections each include one or more pullwires attachedthereto, such that each articulation section is configured toindependently articulate in one or more directions with the actuation ofcorresponding pullwire(s). In some embodiments, the articulationsections are in direct contact with each other; in other embodiments,the articulation sections are spaced apart, with additionalnon-articulating sections positioned between them.

One of the challenges with multiple bending catheters is how to anchorthe pullwires of a proximal section while allowing adequate space forthe pullwires of the distal section to extend past this anchor point. Atypical catheter 180 is illustrated in FIG. 28, including a catheter tip182, a distal anchor ring 184, a distal articulation section 186, apullwire 188, a proximal articulation section 181, a proximal anchorring 185, and a bump 183 in the outer diameter (OD) of the cathetershaft at the location of the proximal anchor ring 185. Typically,pullwires 188 are anchored to a fixed location on the catheter tip 182.The pullwires 188 are often soldered or welded to a control ring oranchor ring 184, 185, which is embedded into the wall of the catheter180. There will often be a bump 183 or increase in the OD of thecatheter 180 at the proximal anchor ring 185, where the pullwires 188going to the distal ring 184 need to pass over, under, or through theproximal ring 185.

In one embodiment of the present disclosure, the load distributionmechanisms described above are used in a double-bending catheter havingan omnidirectional distal section and a single-plane proximalarticulation section without a proximal solder. FIGS. 29A-29C illustrateone embodiment of a catheter 190 with a shaft 192 (or “sidewall”) andmultiple pullwires 194, configured to be a double bending catheterhaving load distribution. All four groups of pullwires 194 are made upof three individual wires 194. The fourth wires are placed centrallybetween the first three wires in the distal articulation section, asshown in FIG. 29A. When distal articulation is required toward the 12o'clock position, all three group 1 wires are pulled uniformly. Whenarticulation towards 4 o'clock is required, all three group 3 wires arepulled uniformly. When articulation towards 6 o'clock is required, allthree group 3 wires and all three group 2 wires are pulled uniformly.The group 4 wires are not used to actuate the distal bend.

In the proximal articulation section of the catheter 190, shown in FIG.29B, wire groups 1, 2, and 3 all merge together at one side of thecatheter shaft 192, and wire group 4 merges together directly opposite.This transition of the articulation wires 194 from being uniformlypositioned in the articulation section to being closely positioned wherearticulation is not intended or being closely positioned to control adegree of freedom of another bend is described in U.S. Pat. No.8,894,610, which is fully incorporated by reference. To achievecontrolled proximal articulation, wire tension may be applied to wiregroup 4, or wire tension may be applied to wire groups 1, 2, and 3simultaneously. If distal articulation is desired, wire tension can beapplied to wire groups 1, 2, or 3 but must be counterbalanced with wiretension on wire group 4 to prevent unwanted proximal articulation.

The designs presented in U.S. Pat. No. 8,894,610 rely on all wiresconverging at one side of the shaft to minimize shaft deflection. Incontrast, the embodiment of the multi-bend catheter 190 presented hereredirects the pullwires 194 in the proximal non-articulating shaft 192,as shown in FIG. 29C. Therefore, wire groups 1, 2, 3, and 4 are allequally distributed in the proximal shaft 192, resulting in no bendingmoment in the shaft 192 when any of the 4 groups are tensioned.

Referring now to FIGS. 30A and 30B, an alternative embodiment of amulti-bend catheter 200 may include a catheter shaft 202 and multiplepullwires 204. In this embodiment, the catheter 200 may include only onepullwire 204 (instead of the three wires) in each of the pullwire groups1, 2, and 3. Pullwire group 4 still includes three pullwires 204.Therefore, this alternative embodiment includes a total of six wires.Wires 1, 2, and 3 are equally positioned in the distal bend (FIG. 30A)and are co-located in the proximal bend (FIG. 30B). The three pullwires204 of group 4 are spread uniformly between the three distal pullwires204 in the distal section (FIG. 30A) and combined on the opposite sideof the distal wires 204 in the proximal bend (FIG. 30B). This design hasthe same bending capability as the design presented in FIGS. 29A-29C,except that this design cannot isolate the proximal portion of the shaft202. The proximal shaft 202 may thus be made of stiffer material or mayemploy the unirail design to minimize unwanted deflection.

In the multi-bend catheter embodiments described immediately above, theproximal articulation section is unidirectional. That is, it can onlybend in one plane. In some alternative embodiments, it may beadvantageous to have a catheter with omnidirectional distal and proximalarticulation capabilities.

Referring now to FIGS. 31A and 31B, one embodiment of anomni-directional, multi-bend catheter 210 is illustrated in simplifiedform. FIG. 31A shows the catheter 210 in a straight configuration, andFIG. 31B shows the catheter 210 in a double-bend configuration. Asillustrated in both figures, the catheter 210 may include a distalarticulation section 212, a proximal articulation section 214 and ashaft section 216. The dotted lines labeled “A,” “B,” and “C” illustratesections through the catheter 210, which are illustrated in differentembodiments in FIGS. 32A-32C and 33A-33C. The shaft section 216 is aproximal portion of the catheter 210 and may also be referred to hereinas a “proximal shaft section” or “proximal shaft portion.”

Referring now to FIGS. 32A-32C, one embodiment of the multi-bendcatheter 210 is illustrated, with six pullwires 218 organized in threegroups of two. In the distal articulation section 212 (FIG. 32A),pullwires 218 paired together do not need to be touching but arepositioned adjacent to each other. The pullwires 218 are then spread outequally about the shaft in the proximal articulation section 214 (FIG.32B), to distribute tension. Finally, all the pullwires 218 are groupedtogether on one side of the catheter along the shaft section 216 (FIG.32C)—in other words, the shaft section 216 has a unirail configuration.

Pulling on wires 1 a and 1 b will articulate the distal articulationsection 212, while not affecting the proximal articulation section 214or the shaft section 216. However, if bending of the proximalarticulation section 214 is desired, pullwires 3 b and 2 a may betensioned, and it would not affect the bend in the distal articulationsection 212, because in that section, pullwires 3 b and 2 a arepositioned 180° opposite each other. In this way, the same pullwires mayextend through, and couple to, each articulation section while beingarranged such that independent articulation of each articulation sectioncan be achieved with selective tensioning of the various pullwires.

The articulation capability of the catheter 210 in FIGS. 32A-32Cincludes the following articulations. For distal articulation toward 12o'clock, pull 1 a and 1 b. For distal articulation toward 4 o'clock,pull 2 a and 2 b. For distal articulation toward 8 o'clock, pull 3 a and3 b. For distal articulation toward 6 o'clock, pull 2 a, 2 b, 3 a, and 3b. For distal articulation toward 10 o'clock, pull 1 a, 1 b, 3 a and 3b. For distal articulation toward 2 o'clock, pull 2 a, 2 b, 1 a, and 1b. In all these articulations of the distal articulation section 212,the proximal articulation section 214 will not bend, because thepullwires 218 being pulled are located 180° opposite to one another inthe proximal articulation section 214.

For proximal articulation toward 12 o'clock, pull 2 a and 3 b. Forproximal articulation toward 4 o'clock, pull 3 a and 1 b. For proximalarticulation toward 8 o'clock, pull 2 b and 1 a. For proximalarticulation toward 6 o'clock, pull 1 a, 2 b, 3 a, and 1 b. For proximalarticulation toward 10 o'clock, pull 2 a, 2 b, 1 a, and 3 b. Forproximal articulation toward 2 o'clock, pull 3 a, 3 b, 2 a, and 1 b. Inall of these articulations of the proximal articulation section 214, thedistal articulation section 212 will not bend, because the pullwires 218being tensioned are 180° opposite one another in the distal articulationsection 212.

FIGS. 33A-33C illustrate an alternative embodiment of a multi-bendcatheter 220, with a distal articulation section 222 (FIG. 33A), aproximal articulation section 224 (FIG. 33B), and a shaft section 226(FIG. 33C). In this embodiment, rather than using the unirailconfiguration in the shaft section 226, the shaft section 226 instead ismade stiffer, to resist deflection. This stiffer shaft may beaccomplished by using a higher durometer material and/or a differentcatheter shaft braid architecture. With this stiffer architecture, thepullwires 228 may continue through the shaft section 226 in the sameconfiguration as in the proximal articulation section 224.

In another alternative embodiment (not shown), a multi-bending cathetermay include nine pullwires, where each pullwire is attached toindividual motors.

Although the above description is believed to be a complete and accuratedescription of a number of embodiments of articulating steerablecatheter for use in medical or surgical procedures, any suitablevariations on the embodiments described above may be made, withoutdeparting from the scope of the invention. For example, features of oneof the described embodiments may be applied to other embodiments,features may be added to or omitted from a given embodiment, or thelike. Thus, the above description is meant to provide details of variousembodiments only, and it should not be interpreted as limiting the scopeof the invention as it is defined by the claims.

1. A steerable catheter system, comprising: a flexible elongate catheterbody, comprising a catheter wall forming a central lumen, a proximalend, a distal end, an articulating section, and a non-articulatingsection; a drive mechanism at the proximal end of the catheter body; andat least one group of pullwires within the catheter wall extending alonga length of the catheter body, wherein each of the at least one group ofpullwires includes at least two pullwires, and wherein each of the atleast two pullwires is anchored at a first end to the catheter body andat a second end to the drive mechanism, and wherein the at least twopullwires of the at least one group of pullwires are positioned close toone another along the articulating section of the catheter body anddiverge away from one another to reach a more separated distributionalong the non-articulating section.
 2. The steerable catheter system ofclaim 1, wherein the more separated distribution of the at least twopullwires in the non-articulating section comprises a uniformdistribution.
 3. The steerable catheter system of claim 1, wherein theat least one group of pullwires comprises three or more pullwires, andwherein the more separated distribution of the three or more pullwiresin the non-articulating section comprises each pullwire in a given groupbeing positioned less than 180 degrees away from each immediatelyadjacent pullwire in the given group.
 4. The steerable catheter systemof claim 1, wherein the at least one group of pullwires comprises threegroups of pullwires, and wherein each of the three groups of pullwirescomprises at least two pullwires.
 5. The steerable catheter system ofclaim 4, wherein each of the three groups of pullwires comprises atleast three pullwires.
 6. The steerable catheter system of claim 1,further comprising a robotic instrument driver, wherein the drivemechanism comprises a splayer comprising multiple pulleys, wherein eachof the multiple pulleys is attached to one of the at least twopullwires, and wherein each of the multiple pulleys is configured to berotated by a motor in the robotic instrument driver.
 7. The steerablecatheter system of claim 6, wherein each of the pulleys is configured tobe rotated to generate tension in the at least two pullwires, andwherein an increase in tension on all of the at least two pullwirescontributes to deflection of the articulating section of the catheterbody.
 8. The steerable catheter system of claim 7, wherein the tensionon the at least two pullwires contributes to a bending moment in thearticulating section of the catheter body while cancelling the bendingmoment in the non-articulating section.
 9. The steerable catheter systemof claim 1, further comprising a robotic instrument driver, wherein thedrive mechanism comprises a splayer comprising multiple pulleys, whereineach of the multiple pulleys is attached to one group of the at leastone group of pullwires, and wherein each of the multiple pulleysinterfaces with a motor in the instrument driver to increase tension inthe one group of pullwires to articulate the catheter body.
 10. Thesteerable catheter system of claim 9, further comprising a loadbalancing actuation mechanism for facilitating proportional tensioningof each pullwire within at least one group of pullwires.
 11. Thesteerable catheter system of claim 10, where the load balancingactuation mechanism is selected from the group consisting of a two-waywhiffletree, a three-way whiffletree, an elastic pullwire, a two-waydifferential and a three-way differential.
 12. The steerable cathetersystem of claim 1, wherein the catheter body has a cylindrical shape.13. The steerable catheter system of claim 1, wherein the at least twopullwires of the at least one group of pullwires spiral around thecatheter body along a divergence section, disposed between thearticulating section and the non-articulating section, to transitionfrom their positions in the articulating section to their positions inthe non-articulating section.
 14. A multiple-bend steerable catheter,comprising: a flexible elongate catheter body, comprising: a catheterwall forming a central lumen; a proximal end; a distal end; a distalarticulating section at the distal end of the catheter body; a proximalnon-articulating section at the proximal end of the catheter body; and aproximal articulating section located between the distal articulatingsection and the proximal non-articulating section; and multiplepullwires within the catheter wall fixed to the distal end of thecatheter body and extending along the catheter body to the proximal end,wherein the multiple pullwires are configured in groups of at least twopullwires each, and wherein the at least two pullwires of each group arepositioned closer to one another in the distal articulation section thanin the proximal articulation section.
 15. The multiple-bend steerablecatheter of claim 14, wherein the multiple pullwires comprise threegroups of two pullwires each, wherein the pullwires in each group arelocated close to one another in the distal articulating section, andwherein the pullwires in each group are located directly across from oneanother in the proximal articulating section.
 16. The multiple-bendsteerable catheter of claim 15, wherein all of the multiple pullwiresare located along one side of the catheter body in the proximalnon-articulating section.
 17. The multiple-bend steerable catheter ofclaim 15, wherein the pullwires in each group are located directlyacross from one another in the proximal non-articulating section, andwherein the proximal non-articulating section of the catheter body isstiffer than the distal articulating section and the proximalarticulating section.
 18. The multiple-bend steerable catheter of claim14, wherein the at least two pullwires in each group of pullwires arelocated in first circumferential positions along the distal articulatingsection, second circumferential positions along the proximalarticulating section, and third circumferential positions along theproximal non-articulating section, and wherein the secondcircumferential positions are farther apart from one another than thefirst circumferential positions.
 19. The multiple-bend steerablecatheter of claim 18, wherein the third circumferential positions arethe same as the second circumferential positions, and wherein theproximal non-articulating section of the catheter body is stiffer thanthe distal articulating section and the proximal articulating section.20. The multiple-bend steerable catheter of claim 18, wherein themultiple pullwires comprise twelve pullwires, comprising: a firstcollection of nine pullwires grouped together in the secondcircumferential position on one side of the catheter body in theproximal articulating section, wherein the nine pullwires are separatedinto three groups of three pullwires in the first circumferentialposition, with each of the three groups separated from the other twogroups by 120 degrees in the distal articulating section, and whereinone pullwire from each of the three groups of pullwires is positioned120 degrees from the other two pullwires from each of the three groupsin the third circumferential position in the proximal non-articulatingsection; and a second collection of three pullwires uniformly positionedaround the catheter body in the first circumferential position in thedistal articulating section and in the second circumferential positionin the proximal non-articulating section, wherein the three pullwiresare distributed to an opposite side of the catheter body from the ninewires in the second circumferential position in the proximalarticulating section.
 21. The multiple-bend steerable catheter of claim20, wherein the distal articulating section is configured to articulatewhen one or two of the three groups of the first collection of ninepullwires are tensioned with an amount of force equal to an amount offorce applied to the second collection of three pullwires.
 22. Themultiple-bend steerable catheter of claim 20, wherein the proximalarticulating section is configured to articulate when the secondcollection of three pullwires is pulled in a first direction uniformlyor when the first collection of nine pullwires is pulled in a second,opposite direction uniformly.
 23. The multiple-bend steerable catheterof claim 18, wherein the multiple pullwires comprise six pullwires,comprising: a first collection of three pullwires positioned toarticulate the distal articulating section, such that they are uniformlypositioned around the catheter body in the distal articulating sectionand positioned to one side of the catheter body in the proximalarticulating section; and a second collection of three pullwirespositioned to articulate the proximal articulating section, such thatthey are uniformly positioned around the catheter body in the distalarticulating section and distributed to one side of the catheter body inthe proximal articulating section at 180 degrees opposite the firstcollection of three pullwires.
 24. The multiple-bend steerable catheterof claim 23, wherein the distal articulating section is configured toarticulate when one or two of the first collection of pullwires aretensioned with an amount of force equal to an amount of force applied tothe second collection of three pullwires.
 25. The multiple-bendsteerable catheter of claim 23, wherein the proximal articulatingsection is configured to articulate when the second collection of threepullwires is pulled in a first direction uniformly or when the firstcollection of three pullwires is pulled in a second, opposite directionuniformly.
 26. The multiple-bend steerable catheter of claim 18, whereinthe multiple pullwires comprise six pullwires, comprising three pairs oftwo pullwires each, wherein each of the three pairs of pullwires isspaced 120 degrees apart from the other two pairs of pullwires aroundthe catheter body in the first circumferential position in the distalarticulating section, and wherein the two pullwires of each of the threepairs separate from one another and are positioned 180 degrees oppositeeach other around the catheter body in the second circumferentialposition in the proximal articulating section.
 27. The multiple-bendsteerable catheter of claim 26, wherein all six pullwires are positionedon one side of the catheter body in the third circumferential positionin the non-articulating proximal section.